1. Field of the Invention
This invention relates to a bit holder, particularly to one including a shank provided with a combining hole, and a bit sleeve provided with a through hole. In combining a bit with the bit holder, the bit is inserted through the through hole of the bit sleeve, and then the male threads of the bit sleeve are engaged with the female threads of the shank. Then an auxiliary tool is fitted around a circular circumference of the bit sleeve, which is successively rotated to combine threadably with the combining hole of the shank, with the lower portion of the bit sleeve pressing an upper portion of the bit so as to minimize the tolerance of the gap between the bit and the shank. Thus the bit sleeve never departs from the shank, and the bit never swings so that the bit can drive a screw effectively and smoothly into an object.
2. Description of the Prior Art
FIGS. 1˜3 show three sorts of conventional bit holders, which commonly include a shank 1 and a bit 2.
The shank 1 is provided with a combining hole 10 formed in its front end for being just tightly fitted with a shank 20 of the bit 2. In FIGS. 1 and 2, a lock ball hole 12 is bored on a wall 11 of the combining hole 10 for fitting with a lock ball 13 that is further surrounded by a sleeve 14. In FIG. 3, the wall 11 of the combining hole 10 is previously finished with a C-shaped lock groove 12A employed to engage with a C-shaped lock washer 13A. Either of the two engagements between the lock ball hole 12 and the lock ball 13 and between the C-shaped lock groove 12A and the C-shaped lock washer 13A mentioned previously needs a little space for the lock ball 13 and the C-shaped lock washer 13A to flexibly move about so as to keep the bit 2 conveniently pulled out or plugged in the shank 1.
Next, as shown in FIG. 4, a fourth conventional bit holder is provided with a hole 15 bored in the shank 1 to communicate with the combining hole 10, and a C-shaped lock washer 16 used to fit in the C-shaped lock groove 12A. As the bit 2 is to be pulled out, an auxiliary tool 3 can be inserted into the hole 15 to push upwards so as to release the bit 2 from the shank 1.
In the four conventional bit holders described above, the bit 2 is provided with an annular groove 21 formed around the shank 20 for being fitted with the lock ball 13 or the C-shaped lock washers 13A and 16 so as to keep the bit 2 fixed thereof. In addition, the annular groove 21 can let the lock ball 13 and the C-shaped lock washers 13A and 16 move properly in the lock ball hole 12 and the C-shaped lock groove 12A respectively, so that the bit 2 can be smoothly plugged in or released from the shank 1.
In order to enable the lock ball 13 and the C-shaped lock washers 13A and 16 to properly move about so as to keep the bit 2 smoothly inserted in or pulled out of the shank 1, the thickness (L) of the wall 11 must be sustained in an appropriate range. The conventional bit holders shown in FIGS. 1˜3 has a rather large outer diameter (more than 7 mm), unsuitable for being utilized in an automatic screwdriver with a screw band. The fourth conventional bit holder shown in FIG. 4 is purposely designed to lessen the outer diameter of the shank 1 so as to be usable for an automatic screwdriver. However, when the bit 2 is fitted in the combining hole 10 of the shank 1, the bit 2 is blocked such tightly by the C-shaped lock washer 16 that it can not be manually plucked out of the combining hole 10. So the hole 15 is employed to be inserted by an auxiliary tool to help pushing the bit out on basis of leverage. But, with the hole 15 bored in the shank 1, the strength of the shank 1 is to be downgraded, apt to make the shank 1 deformed or broken at the location of the hole 15, posing a loss or a burden to consumers.
FIG. 5 shows a fifth conventional bit holder, which also includes the shank 1 provided with the combining hole 10 formed in its front end, and two lock ball holes 12 cut in the wall 11 of the combining hole 10 for being fitted with the lock balls 13.
In addition, a compression spring 14 is mounted around the wall 11, with its one end pressing on an annular surface 111 of the wall 11 and the other one pressing on an annular surface 140 of a sliding sleeve 14A, enabling it confined between the wall 11 and the sliding sleeve 14A. An annular C-shaped lock washer 112 is put around the front outer circumference of the wall 11 of the combining hole 10 to prevent the sliding sleeve 14A from coming off the shank 1. The sliding sleeve 14A is provided with an annular oblique surface 141 formed around its front end for keeping the bit 2 from being tightly squeezed by the lock ball 13 so as to easily pull it out thereof.
By means of the sliding sleeve 14A, the conventional bit holder shown in FIG. 5 enables the bit 2 easily plugged in or pulled out of the shank 1. However, as the outer diameter (d1) of the sliding sleeve 14A is much larger than the outer diameter (d2) of the shank 1, such a two-part-assembled bit holder can hardly be utilized in an automatic screwdriver. The automatic screwdriver commonly used nowadays is re-positioned by a rebounding force of a compression spring after driving a screw into an object. But, because the circumference of the bit holder is wrapped by screw band holes and their annular circumference, the relevant component of the automatic screwdriver is difficult to come back to its original position owing to a large diameter of the bit holder.
Next, as shown in FIG. 6, a sixth conventional bit holder invented by the inventor of the present invention and disclosed in Taiwan Patent No. 091211788 is devised to overcome the defects existing in the five conventional bit holders mentioned above. It also includes a shank 1 provided with a combining hole 10, a bit 2, and an bit sleeve 3.
The shank 1 is provided with an annular locking groove 101 formed in its wall 100, and an annular oblique surface 102 formed around its outer end.
The bit 2 is provided with a rear portion 22 shaped geometric without any groove formed in its surface for engaging with the shank 1, a front portion 23 including a bit head 230, and an annular petal-shaped portion 24 formed around a surface of the rear portion. The rear portion 22 has a larger diameter than that of the front portion 23.
The bit sleeve 3 is provided with an annular elastic circumference 30 cut with plural grooves 31 employed to enable the annular elastic circumference 30 to be more flexible. The annular elastic circumference 30 has an annular projection 32 formed around its rear end to fit in the annular locking groove 101 of the combining hole 10 of the shank 1.
As the bit sleeve 3 is made of plastics, it must keep the bit 2 tightly fixed with the shank 1 without shaking before operating a hand tool. However, when the bit 2 is operated to whirl with a high speed, it is to get heated to soften the bit sleeve 3 so as to weaken the engagement between the bit sleeve 3 and the bit 2, posing the bit 2 to depart from the shank 1.
And, if the bit 2 is to be loosened from the shank 1, it has to be pulled open by an extra tool, possible to damage the bit sleeve 3. Thus a lot of the bit sleeves 3 must be prepared for spares while operating a hand tool with the bit holder.
Moreover, as the bit sleeve 3 is made of plastics, a rather great tolerance is practically created in engagement of the bit sleeve 3 and the bit 2, posing an unacceptable gap between the bit 2 and the shank 1 so that the bit 2 is to swing while being driven to rotate with a high speed by a hand tool, unable to smoothly and precisely drive a screw into an object.